A degree-of-risk calculation apparatus for calculating the degree of potential risk around a host vehicle has been proposed (see International Publication No. 2012/032624). According to International Publication No. 2012/032624, based on information from an obstacle detection device, the degree-of-risk calculation apparatus changes the mesh setting for gridded areas around the host vehicle, and thereby calculates the risk potentials respectively for the intersections, or in the gridded areas, in the mesh. Accordingly, based on the thus-calculated risk potentials, the degree-of-risk calculation apparatus sets the target route of the host vehicle.
Since the risk potentials are calculated respectively for all the gridded areas around the host vehicle, a problem arises in which when many obstacles are detected, the arithmetic load increases, and it takes longer to calculate the degree of risk.